1. Field of the Invention
The present invention relates generally to methods of bonding and sealing together metal parts. In particular, the present invention relates to processes of fabricating and repairing hollow beryllium structures, that must be leak tight and that experience temperature cycles, through high temperature isostatic pressure bonding.
2. Background Information
Typically beryllium vessels have been formed by welding or brazing using a filler metal, such as aluminum or silver. The problem with such vessels is that the coefficient of thermal expansion (CTE) of the filler metal is substantially different from that of the bulk beryllium. The use of a filler metal for joining results in low strength properties. Although these methods can be adequate under some circumstances for systems that require lower strength properties and do not go through temperature cycling, they will not guarantee leak tightness, particularly with large or complex beryllium containers.
Furthermore, these bonding methods should not be used with pressure vessels having high internal pressures and that are subjected to large temperature variations, ΔT. One example of such a vessel is a space flight Cryogenic Thermal Storage Unit (TSU). Cryogenic TSUs experience a large temperature swing (ΔT≈300 K), and require large factors of safety in the bond area to meet the aerospace requirements.
A need therefore exists for improved bonding methods that provide the necessary reliability.